Development of novel candidate therapeutics for treating osteoarthritis and hyperpigmentation

Abstract

Human life span is increasing in modern society. More recently, advances in drug discovery are a contributing factor for human life extension. Moreover, people invest more time and expenditure in beauty treatments in accordance with lifespan extension. Major focuses of drug discovery are degenerative diseases (eg., osteoarthritis) and cosmetics (eg., whitening agents). Despite a large amount of research about the degenerative disease, such as osteoarthritis, and the whitening of skin pigmentation, spanning several decades, there are no complete recovery drugs. Discovery of novel drugs that target new cellular targets or mechanisms would have the potential to be developed as treatments.

Osteoarthritis (OA), which is predominantly characterized by extracellular matrix degradation, is caused by an excessive accumulation of zinc content in chondrocytes, which activates matrix-degrading enzymes and leads to cartilage destruction. Thus, maintaining a constant state of cellular zinc homeostasis is essential for preventing OA progression. Based on the recently described 'Zinc-ZIP8-MTF1 axis' which cause a catabolic cascade in the cartilage of OA patients, I have screened a chemical library to discover compounds that effectively inhibit zinc (Zn2⁺) influx into chondrocytes. In this study, I screened 2,000 compounds, based on intracellular zinc detection using the probe TSQ (N-(6-Methoxy-8-quinolyl)-p-toluenesulfonamide, Enzo). One most promising hit compounds, termed ND-2, significantly inhibited Zn2⁺ influx in both ATDC5 ZIP8 overexpressed chondrocytes and mouse primary chondrocytes. Furthermore, the hit compound ND-2 downregulated the expression of MMP3, MMP13 and ADAMTS5 in pathological conditions (via treatment of IL-1β, pro-inflammatory cytokine in OA pathogenesis). Interestingly ND-2 also blocked the translocation of transcription factor MTF-1, which is a major mediator of the zinc influx-induced inflammatory response. This study indicated that potential ND-2 may be further developed as a drug candidate for OA.

Hyper-pigmentation disorders, which are caused by the dysregulation of melanin production, can accumulate excessive levels of pigmentation that cause conditions, such as melasma, age spots and sites of solar keratosis and is found preferentially in aging skin in older adults. Thus, there is a continual need to develop novel and effective anti-pigmentation agents for the prevention of hyper-pigmentation disorders. Additionally, skin color changes can be problematic for cosmetic reasons and have created an important global market for skin brightening products. Known skin brightening products and therapeutic agents include hydroquinon, retinoids and tyrosinase inhibitors. To develop novel anti-pigmentation agents, I have performed zebrafish-based in vivo assays measuring melanin contents and tyrosinase activity. In this study, amino levulinic acid (ALA) derivatives were tested. As a result, the derivative, ALACELL, showed anti-pigmentation effects at a concentration of 10µM. These data demonstrate the potential of ALACELL to be developed as a candidate novel melanin modulator for pharmaceutical and cosmetic skin whitening applications.